title: Nuclear accumulation of calcineurin B homologous protein 2 (CHP2) results in enhanced proliferation of tumor cells.
abstract: The interaction between calcineurin B homologous protein 2 (CHP2) and Na(+) /H(+) exchanger 1 (NHE1), two membrane proteins, is essential for protecting cells from serum deprivation-induced death. Although four putative EF-hands in CHP2 had been predicted for years, Ca²(+) -binding activities of these motifs have not been tested yet, their role in this process remain poorly understood. To identify Ca²(+) -binding motifs required for the stable formation of CHP2/NHE1 complexes, we developed a mutagenesis-based assay in PS120 cells. We found that (45) Ca²(+) bond to two EF-hand motifs (EF3 and 4) of CHP2 proteins with high affinity. Complex formation between CHP2 and the CHP2 binding domain of NHE1 resulted in a marked increase in the Ca²(+) -binding affinity of CHP2. Co-immunoprecipitation and distribution of GFP-tagged CHP2-EF3m/4m also indicated that Ca²(+) affected the membrane location of CHP2 to interact with NHE1. The C-terminal region of CHP2 contains a nuclear export sequence (NES). When the six leucines of NES were mutated to alanines, the resulting CHP2 protein was predominantly localized to the nucleus. Furthermore, mutation of the NES resulted in enhanced proliferation and oncogenic potential of HeLa cells. Together, these results show that calcium and NES control the subcellular distribution of CHP2 and then distinctively regulate cell proliferation.
authors.affiliation: State key Laboratory of Experimental Hematology, Institute of Hematology and Hospital of Blood Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Tianjin 300020, China.
authors.forename: Qing-Hua
authors.initials: QH
authors.lastname: Li
authors.forename: Li-Hong
authors.initials: LH
authors.lastname: Wang
authors.forename: Ya-Ni
authors.initials: YN
authors.lastname: Lin
authors.forename: Guo-Qiang
authors.initials: GQ
authors.lastname: Chang
authors.forename: Hua-Wen
authors.initials: HW
authors.lastname: Li
authors.forename: Wei-Na
authors.initials: WN
authors.lastname: Jin
authors.forename: Rong-Hua
authors.initials: RH
authors.lastname: Hu
authors.forename: Tian-Xiang
authors.initials: TX
authors.lastname: Pang
mesh_terms: D000595:Amino Acid Sequence; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000378:metabolism*; D002461:Cell Line, Transformed; D049109:Cell Proliferation; D020832:EF Hand Motifs / Q000235:genetics*; D006367:HeLa Cells / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals / Q000737:chemistry* / Q000502:physiology; D016415:Sequence Alignment; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*
chemical_list: C469743:CHP1 protein, human; D002135:Calcium-Binding Proteins; D027682:Cation Transport Proteins; D019913:Nuclear Localization Signals; C490998:SLC9A1 protein, human; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers